Programmable multi-chip module

ABSTRACT

A multi-chip module comprising a low-temperature co-fired ceramic substrate having a first side on which are mounted active components and a second side on which are mounted passive components, wherein this segregation of components allows for hermetically sealing the active components with a cover while leaving accessible the passive components, and wherein the passive components are secured using a reflow soldering technique and are removable and replaceable so as to make the multi-chip module substantially programmable with regard to the passive components.

RELATED APPLICATIONS

[0001] The present application is a division of an earlier-filed,copending U.S. non-provisional patent application titled PROGRAMMABLEMULTI-CHIP MODULE, Ser. No. 10/253,851, filed Sep. 23, 2002. The presentapplication claims priority benefit of the identified application, andhereby incorporates the identified application by reference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT PROGRAM

[0002] The present invention was developed with support from the U.S.government under Contract No. DE-AC04-01AL66850 with the U.S. Departmentof Energy. Accordingly, the U.S. government has certain rights in thepresent invention.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates broadly to multi-chip modules andother similar electronic microcircuitry and methods of manufacturing thesame. More particularly, the present invention concerns a multi-chipmodule comprising a low-temperature co-fired ceramic substrate having afirst side on which are mounted active components and a second side onwhich are mounted passive components, wherein this segregation ofcomponents allows for hermetically sealing the active components with acover while leaving accessible the passive components, and wherein thepassive components are secured using a reflow soldering technique andare removable and replaceable so as to make the multi-chip modulesubstantially programmable with regard to the passive components.

[0005] 2. Description of the Prior Art

[0006] Many electronic systems include microcircuits designed for aspecific product application. Unfortunately, both the active componentsand the passive components of such a microcircuit must typically beirreversibly committed to a particular design early in themicrocircuit's development cycle. As a result, if one or more of thesecomponents of the original design do not produce desired results, a newdesign cycle must be initiated.

[0007] A multi-chip module (MCM) is a type of microcircuit, andtypically includes a number of active components, such as, for example,integrated circuits (ICs), transistors, and diodes, and a number ofpassive surface mount components, such as, for example, capacitors,resistors, inductors, or memory modules, electrically interconnectedwith high-density lines. The active components are typicallyinterconnected by wire bonding to ceramic substrates (MCM-C), laminatesubstrates (MCM-L), or deposited thin film substrates (MCM-D). Both theactive and the passive components are typically mounted on one side ofthe substrate so as to be intermingled in a non-segregated manner, andthen hermetically sealed beneath a cover.

[0008] Unfortunately, prior art MCMs suffer from a number of problemsand disadvantages, including, as mentioned, that both the active and thepassive components, being sealed beneath the cover, are substantiallyinaccessible. As a result, where the design is later determined to beflawed, the MCMs cannot be modified to a new design and must bediscarded. Furthermore, intermingling the active and the passivecomponents can result in longer electrical interconnections whichresults in a correspondingly slower processing speed.

[0009] Due to the above-identified and other problems and disadvantagesin the art, a need exists for an improved microcircuit that betterfacilitates efficient and convenient design, testing, and modification.

SUMMARY OF THE INVENTION

[0010] The present invention overcomes the above-described and otherproblems and disadvantages in the prior art with an MCM manufactured soas to allow for substantial programmability in that at least some of aplurality of components of the MCM are and remain removable andreplaceable throughout the design and testing process.

[0011] In a preferred embodiment, the MCM broadly comprises a substrate;one or more active components; a cover; and one or more passivecomponents. The substrate is a low-temperature co-fired ceramic (LTCC)substrate, and presents a first side and a second side. The activecomponents can include ICs, transistors, and diodes and are wire bondedto the first side of the substrate. The cover protects the mountedactive components by hermetically sealing over them. The passivecomponents are, for example, capacitors, resistors, inductors, or memorymodules, and are reflow soldered to the second side of the substrate.Thus, the passive components are not hermetically sealed under thecover, and therefore remain accessible.

[0012] The active and the passive components are electricallyinterconnected with vias or through-holes in the substrate or with edgeconnectors. Because the active and the passive components are notmounted or otherwise secured in an intermingled and non-segregatedmanner on the same side of the substrate, the electricalinterconnections between the active components are not required to avoidthe passive components or otherwise be longer than absolutely necessaryand can therefore be made shorter than is typically possible in priorart MCMs. These shorter interconnections advantageously result incorrespondingly improved performance.

[0013] The described MCM can be designed, tested, and modified asfollows. First, an interconnection network is fabricated on thesubstrate. Then the active components are attached and wire bonded tothe first side of the substrate. Next, the active components arehermetically sealed under the cover. Then the passive components aremounted to the second side of the substrate using a reflow solderingtechnique which allows for removing and replacing the passive componentsas desired. Next, the MCM is tested for a desired performance. Lastly,as desired, certain of the passive components can be removed andreplaced using conventional solder reworking techniques so as to achievethe desired performance. With special test fixtures, the passivecomponents can be left off the MCM, and the MCM can be functionallytested. Passive components can then be selected and attached to the MCMfor a specific circuit design.

[0014] Thus, it will be appreciated that the present invention providesa number of substantial advantages over the prior art, including, forexample, segregating the passive components from the hermetically sealedactive components, thereby facilitating removal and replacement of thepassive components and making the MCM substantially programmable. Thisadvantageous ability allows developers to test a variety of componentvalues prior to committing to a finalized design, thereby shorteningtotal design cycle time by minimizing circuit redesign and rebuild time.Furthermore, this segregation of components facilitates shorterelectrical interconnections to result in correspondingly improvedperformance for the active components.

[0015] These and other important features of the present invention aremore fully described in the section titled DETAILED DESCRIPTION OF APREFERRED EMBODIMENT, below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A preferred embodiment of the present invention is described indetail below with reference to the attached drawing figures, wherein:

[0017]FIG. 1 is an exploded elevation view of an MCM constructed inaccordance with a preferred embodiment of the present invention;

[0018]FIG. 2 is an isometric view of the MCM of FIG. 1;

[0019]FIG. 3 is a high level flow chart of steps involved inmanufacturing the MCM of FIG. 1;

[0020]FIG. 4a is a low level flow chart of steps involved inmanufacturing the MCM of FIG. 1; and

[0021]FIG. 4b is a continuation of the low level flow chart of FIG. 4a.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0022] Referring to FIG. 1, an MCM 10 is shown constructed in accordancewith a preferred embodiment of the present invention. The MCM 10 ismanufactured so as to allow for a substantial degree of programmabilityin that at least some of the components of the MCM 10 are and remainremovable and replaceable through the design and testing process.

[0023] As illustrated, the MCM 10 broadly comprises a substrate 12; oneor more active components 14; a cover 16; and one or more passivecomponents 18. The substrate 10 provides a mounting structure havingparticular desired electrical, mechanical, and other characteristics,and is preferably a low-temperature co-fired ceramic substrate. Thesubstrate 10 presents a first substantially planar side 22 and a secondsubstantially planar side 24.

[0024] The one or more active components 14 are electrically activecomponents, such as, for example, ICs. The active components 14 aremounted or otherwise secured, such as, for example, by wire bonding, tothe first side 22 of the substrate 10. The cover 16 is a substantiallyconventional mechanism for protecting the mounted active components 14from environmental extremes and solder flux. In a conventional manner,the cover 16 is hermetically sealed to the substrate 10 over the activecomponents 14.

[0025] The one or more passive components 18 are electrically passivecomponents, such as, for example, capacitors, resistors, inductors, ormemory modules. The passive components 18 are removably and replacablymounted or otherwise secured, such as, for example, by surface mountingusing a reflow soldering technique, to the second side 24 of thesubstrate 10. Thus, the passive components 18 are not hermeticallysealed under the cover 16 with the active components 14, and thereforeremain more easily accessible.

[0026] The aforementioned reflow soldering technique is a well-knowntechnique for achieving a metal-to-metal joining. In a typical reflowsoldering process, solder is first applied or otherwise interposedbetween solder sites of metal members to be joined. A heating element isthen used to apply heat to the soldering sites, thereby melting thesolder. The heating element is then removed and the solder allowed tosolidify, thereby physically and electrically joining the metal members.Reflow soldering has been used extensively in the fabrication andmounting of electronic components.

[0027] The active and the passive components 14,18 are electrically andotherwise operatively interconnected using one or more edge connectors28 or vias 29 or other through-holes provided in the substrate 10.Because the active and the passive components 14,18 are not mounted orotherwise secured so as to be intermingled and non-segregated on thesame side of the substrate 10, the electrical interconnections betweenthe active components 14 are not required to avoid the passivecomponents 18 or otherwise be longer than absolutely required, and cantherefore be made shorter than is typically possible in prior art MCMs.These shorter interconnections advantageously result in correspondinglyimproved performance.

[0028] Referring also to FIG. 3, manufacturing the MCM 10 proceeds asfollows. First, an interconnection network is fabricated on thesubstrate 10 (as represented by box 30); then the active components 14are mounted to the first side 22 of the substrate 10 (box 32); next, theactive components 14 are hermetically sealed under the cover 16 (box34); then the passive components 16 are mounted to the second side 24 ofthe substrate 10 in a manner allowing them to be removed and replaced asdesired or necessary (box 36); next the MCM 10 is tested for a desiredperformance (box 38); and lastly, as necessary, certain of the passivecomponents 18 are removed and replaced so as to achieve the desiredperformance (box 40). When such removal and replacement is performed,the step of testing (box 38) may be repeated.

[0029] In greater detail, referring also to FIGS. 4a and 4 b, the stepof fabricating the interconnection network (box 30) proceeds as follows.First, tape layers are cut from a roll of the LTCC substrate material(box 42). Then vias are formed in the substrate material so as to allowfor electrically interconnecting the first and second sides 22,24 of thesubstrate 10 (box 44). Next, via fill is printed and dried (box 46), andconnectors are printed and dried (box 48). Then the layers of theinterconnection network are collated and laminated (box 50). Next, allthe conductors are cofired and additional conductors are printed, dried,and fired (box 52), and the resistors are printed, dried, and fired (box54). Then the resistors are laser trimmed to specific values (box 56).Lastly, the interconnection network is laser scribed or sawed (box 58).

[0030] The step of mounting the active components 14 to the first side22 of the substrate 10 (box 32) proceeds as follows. First, theinterconnection network is cleaned to facilitate proper mounting (box62). Then an adhesive, such as, for example, epoxy, is dispensed onappropriate locations on the first side 22 (box 64). Next, the activecomponents 14 are positioned, such as, for example, by pick-and-placeautomation, so as to contact the epoxy (box 66). Then the epoxy isallowed time to cure (box 68). Next, the active components 14 are wirebonded (box 70). Thereafter, the cover 16 is positioned and hermeticallysealed over the mounted active components 14 (box 34).

[0031] The step of mounting the passive components 18 to the second side24 of the substrate 10 (box 36) proceeds as follows. First, the solderis dispensed onto the soldering sites (box 78). The solder may be, forexample, 63/37 SnPb solder. Then the passive components 18 arepositioned such as, for example, by pick-and-place automation, over thesolder (box 80). Next, the solder is reflowed (box 82), such as, forexample, by positioning the MCM 10 in a conveyorized convection reflowoven which first preheats the MCM 10 and the properly positioned activeand the passive components 14,18 and then heats to 220° C. to melt thesolder and secure the passive components 18 to the MCM 10. Then the MCM10 is cleaned (box 84), particularly of solder flux residues. Lastly,the MCM 10 is tested for proper electrical operation.

[0032] Thereafter, any inoperative, improperly positioned, or otherwiseundesired passive components 18 can be tested (box 38) and, asnecessary, removed and replaced (box 40) using a conventional reworkingtechnique involving, for example, a hot plate and solder iron or aworkstation that is specifically designed for reworking solderedcomponents. Thus, for example, where the MCM 10 is complete and it isfound that the underlying design is flawed with regard to the values orother characteristics of certain of the passive components 18, thosepassive components 18 can be easily removed and replaced to achieve adifferent performance or operation result.

[0033] It will be appreciated that the programmable MCMs 10 of thepresent invention can replace existing printed circuit or wiring boardassemblies where customizable design capability is desired, and have usein any microcircuit applications in, for example, aerospace, automotive,computer, medical, and consumer electronics.

[0034] From the preceding description, it will be appreciated that thepresent invention provides a number of substantial advantages over theprior art, including, for example, segregating the active components 14from the passive components 18, thereby facilitating removal andreplacement of the passive components 18 and making the MCM 10substantially programmable. This advantageous ability allows developersto test a variety of component values prior to committing to a finalizeddesign, thereby shortening total design cycle time by minimizing circuitredesign and rebuild time. Furthermore, this segregation of components14,18 facilitates shorter electrical interconnections to result incorrespondingly improved performance for the active components 14.

[0035] Although the invention has been described with reference to thepreferred embodiments illustrated in the attached drawings, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims. Itwill be appreciated, for example, that the present invention is notlimited to any particular type or nature of microcircuitry, activecomponents, or passive components, nor does it preclude mounting orotherwise securing one or more active components and passive componentsin an intermingled and non-segregated manner on a same side of thesubstrate. Instead, the present invention is concerned primarily withachieving programmability of at least some of the passive components bysegregating them from the hermetically sealed active components so thatat least the segregated passive components can be removed and replacedas desired using conventional reworking techniques.

[0036] Having thus described the preferred embodiment of the invention,what is claimed as new and desired to be protected by Letters Patentincludes the following:

1. A method of implementing a microcircuit, the method comprising thesteps of: (a) fabricating an interconnection network on a substratehaving a first side and a second side; (b) mounting one or more activecomponents to the first side of the substrate; (c) sealing hermeticallythe one or more active components with a cover; (d) mounting one or morepassive components to the second side of the substrate in such a mannerthat the one or more passive components are removable and replaceable;(e) testing the microcircuit for a desired performance; and (f) removingand replacing, as necessary, one or more of the one or more passivecomponents so as to achieve the desired performance.
 2. The method asset forth in claim 1, wherein step (a) includes— (a₁) cutting one ormore tape layers from a roll of a ceramic tape substrate material; (a₂)drilling one or more holes through the substrate to allow forelectrically interconnecting the one or more active components and theone or more passive components; (a₃) printing and drying a via fill;(a₄) printing and drying one or more connectors; (a₅) collating andlaminating the interconnection network; (a₆) cofiring one or moreconductors; (a₇) printing, drying, and firing one or more conductors andone or more resistors; (a₈) trimming the one or more resistors; and (a₉)scribing the interconnection network.
 3. The method as set forth inclaim 1, wherein step (b) includes— (b₁) cleaning the interconnectionnetwork to facilitate proper mounting of the one or more activecomponents; (b₂) dispensing an adhesive onto one or more predeterminedlocations on the first side of the substrate; (b₃) positioning the oneor more active components so as to contact the adhesive; (b₄) curing theadhesive; and (b₅) wire-bonding the one or more active components. 4.The method as set forth in claim 1, wherein step (d) includes— (d₁)dispensing a solder onto one or more predetermined soldering sites onthe second side of the substrate; (d₂) positioning the one or morepassive components so as to contact the solder; (d₃) reflowing thesolder; and (d₄) cleaning any solder flux residue from the microcircuit.5. The method as set forth in claim 1, wherein the microcircuit is amulti-chip module.
 6. The method as set forth in claim 1, wherein thesubstrate is a low-temperature co-fired ceramic.
 7. The method as setforth in claim 1, wherein the one or more active components are selectedfrom the group consisting of: integrated circuits, transistors, anddiodes.
 8. The method as set forth in claim 1, wherein the one or morepassive components include one or more passive surface mount components.9. The method as set forth in claim 1, wherein the one or more passivesurface components are selected from the group consisting of:capacitors, resistors, inductors, and memory modules.
 10. A method ofimplementing a design for a multi-chip module, the method comprising thesteps of: (a) fabricating an interconnection network on alow-temperature co-fired ceramic substrate having a first side and asecond side; (b) wire-bonding one or more integrated circuits to thefirst side of the low-temperature co-fired ceramic substrate; (c)sealing hermetically the one or more active components with a cover; (d)reflow-soldering one or more passive surface mount components to thesecond side of the low-temperature co-fired ceramic substrate in such amanner that the one or more passive surface mount components areremovable and replaceable; (e) connecting the one or more integratedcircuits with the one or more passive surface mount components throughone or more vias in the low-temperature co-fired ceramic substrate; (f)testing the microcircuit for a desired performance; and (g) removing andreplacing, as necessary, one or more of the one or more passive surfacemount components so as to achieve the desired performance.
 11. Themethod as set forth in claim 10, wherein the one or more passive surfacemount components are selected from the group consisting of: capacitors,resistors, inductors, and memory modules.
 12. A method of implementing amicrocircuit, the method comprising the steps of: (a) fabricating aninterconnection network on a substrate having a first side and a secondside; (b) wire-bonding one or more active components to the first sideof the substrate; (c) sealing hermetically the one or more activecomponents with a cover; (d) mounting one or more passive components tothe second side of the substrate in such a manner that the one or morepassive components are removable and replaceable; (e) testing themicrocircuit for a desired performance; and (f) removing and replacing,as necessary, one or more of the one or more passive components so as toachieve the desired performance.
 13. A method of implementing amicrocircuit, the method comprising the steps of: (a) fabricating aninterconnection network on a substrate having a first side and a secondside; (b) mounting one or more active components to the first side ofthe substrate; (c) sealing hermetically the one or more activecomponents with a cover; (d) reflow-soldering one or more passivecomponents to the second side of the substrate so that the one or morepassive components are removable and replaceable; (e) testing themicrocircuit for a desired performance; and (f) removing and replacing,as necessary, one or more of the one or more passive components so as toachieve the desired performance.
 14. A method of implementing amicrocircuit, the method comprising the steps of: (a) fabricating aninterconnection network on a substrate having a first side and a secondside; (b) mounting one or more active components to the first side ofthe substrate; (c) sealing hermetically the one or more activecomponents with a cover; (d) mounting one or more passive components tothe second side of the substrate in such a manner that the one or morepassive components are removable and replaceable; (e) connecting the oneor more active components with the one or more passive componentsthrough vias in the substrate; (f) testing the microcircuit for adesired performance; and (g) removing and replacing, as necessary, oneor more of the one or more passive components so as to achieve thedesired performance.
 15. A method of implementing a microcircuit, themethod comprising the steps of: (a) fabricating an interconnectionnetwork on a substrate having a first side and a second side; (b)mounting one or more active components to the first side of thesubstrate; (c) sealing hermetically the one or more active componentswith a cover; (d) mounting one or more passive components to the secondside of the substrate in such a manner that the one or more passivecomponents are removable and replaceable; (e) connecting the one or moreactive components with the one or more passive components using one ormore edge connectors; (f) testing the microcircuit for a desiredperformance; and (g) removing and replacing, as necessary, one or moreof the one or more passive components so as to achieve the desiredperformance.